1. Field of the Invention
The present invention relates to various methods and devices for producing spunbonded nonwoven fabrics.
2. Description of Related Art
Thermoplastic polymers which are spun in the molten condition to form fine spun filaments are used as base materials. The extruded filaments are mostly aerodynamically drawn, thus obtaining the desired tenacity. Subsequent to the spinning process, or also with spools being interpositioned, the filaments are deposited on a deposition belt on which they come to rest one over another, forming the spunbonded nonwoven fabric.
German Patent Application DE-AS 1 303 569 describes a method for producing nonwoven fabrics in which the extruded filaments are guided through a duct where they are aerodynamically drawn and subsequently deposited in the form of a nonwoven fabric on a perforated moving support.
To ensure the statistically random deposition of the filaments, a turbulence zone, which supports the crosswise deposition of the filaments, is provided beneath the air guide duct. A very irregular appearance of the nonwoven fabric ensues. A high uniformness of the spunbonded nonwoven fabric is achieved in that several guide ducts are provided one behind the other and in that the filament sheets emerging therefrom are deposited one over another in a layer-like manner to form a nonwoven fabric.
To be able to determine the desired uniformness of the nonwoven fabric and its tenacity in the longitudinal and cross direction, it is known from German Patent Application DE 39 07 215 A1 to design the spinning manifolds together with the filament pull-off device such that they are rotatable. This is also intended to eliminate the disadvantages which arise in the so-called “curtain method” and which can cause individual filaments to overlap in certain regions. In the curtain method, the nonwoven fabric possesses a preferred tenacity in the longitudinal direction, that is in the production direction, while the tenacity values in the cross direction are lower. This is to be compensated for by skewing the spinning manifolds together with the deposition and drawing device.
In addition, it is known from German Patent DE 35 42 660 C2 to achieve a deviation of the air flow beneath the pull-off duct with the aid of a parallelly arranged swivelling device to attain a pendulum motion of the filaments in this manner. The swivelling motion takes place in the moving direction of the deposition belt in the production direction; also usable here are, inter alia, so-called “Coander dishes” as are described, for example, in German Patent DE 24 21 401 C3. However, the provided measures are relatively sluggish so that only slow oscillations of the filament sheet are possible.